1. Field of the Invention
The present invention relates to a method and to an apparatus for automatic access optimization during reading of data words from a random access memory, and in particular to the same utilizing an error correction device.
2. Description of the Prior Art
Larger random access memories, such as, for example, working memories of data processing systems are presently, virtually without exception equipped with installations for error correction. Error correction devices are known in the art in various embodiments (cf. e.g. the German published application No. 2,549,392 and the German published application No. 2,657,826 corresponding to U.S. Pat. No. 4,030,067). Common to all error correction devices is a syndrome generator or syndrome calculator which derives check bits from the data word to be written into the memory in accordance with a specific algorithm which is the basis of the correction code employed, the check bits being input into the memory together with the data word. Subsequent to the reading of a data word from the memory, check bits are again derived in accordance with the same specification and are compared with the check bits read from the memory. The comparison result is designated as a syndrome and represents an information regarding the error situation of the word read from the memory. It is zero if the data word is error-free. A syndrome deviating from zero indicates that errors have occurred. It depends upon the type of correction code employed, in particular upon its redundancy, i.e. upon the number of check bits added to the original data word, as to how many errors are still correctable in a data word and what number of errors can still be ascertained at all.
The assessment of all operations, in conjunction with an error correction, or error recognition, respectively, must be taken into consideration that the probability of the presence of error-free data words is greatest by far, and the probability of the simultaneous occurrence of errors decreases very rapidly with an increasing error number.
The access time in a memory is defined as the time interval between the connection of a read start signal, which initiates a read operation, and the appearance of the read data which become valid by means of a transfer signal at the interface. The time point for the occurrence of the read data validity signal (Dardy) must, as a rule, be geared to the slowest data path, which is composed of several individual components, of which the maximally possible access time for an individual memory cell within a random memory module is under the most unfavorable conditions and the maximum path for the drive signals and read signals are the most important. It is clear that, in this manner, time is frequently wasted. Nevertheless, an individual adaptation of the access time to the conditions actually present in the case of a concrete memory example is only rarely carried out, because, in the case of a possible necessary exchange of memory groups, most frequently new adjustment measures would have to be carried out.